The present invention concerns a sensor for scanning the working distance between cooperating card clothings (also called carding gap), i.e. the actual distance of the points of a card clothing to a machine element facing it. This machine element also can be covered with clothing but could also be represented by a cover element provided with a guide surface instead. The present invention in particular is aimed at measuring the working distance between the main drum and the flats of a revolving flat arrangement, but is not restricted to this lay-out.
The present invention also concerns an "on-line" control system influencing the carding gap i.e. without interrupting the card operation. The present invention is conceived to be applied, but no exclusively, to a revolving flat card.
Significance of the carding gap/starting point:
The carding gap is the distance between a clothing and an element facing the clothing. The size (width) of the carding gap is an important machine parameter characterizing the fibre processing technology as well as the running properties of the machine. The carding gap is set as narrow as possible (being measured in tenths of a millimeter) without taking the risk of a "collision" between the working elements. If uniform processing of the fibres is to be ensured, the gap width is to be maintained equal as far as possible over the full working width of the machine. The working width of a conventional revolving flat card is about one meter, larger cards having been proposed.
The carding gap is influenced by two basic factors, namely the machine settings and the condition of the clothing.
The most critical carding gap is located in the main carding zone, i.e. between the main drum and the revolving flat arrangement. The width of this gap traditionally, since decades, is set using a so-called flexible arch. The setting procedure, however, requires specially trained personnel and the machine cannot be operated while being set. The setting procedure thus normally is repeated only if the machine is re-clothed, or after a clothing service, i.e. after time intervals ranging from several months to up to two years. It is known, however, that the carding performance could be "optimised" if the machine elements were adjusted "on-line" in so far as the unavoidable changes in the state of the clothing could be off-set partially at least by correspondingly adapting the machine settings.